1. Field of the Invention
The present invention relates generally to a new class of hard nano-structured materials, including coatings and bulk solid thereof, and methods of their manufacture. More particularly, the present invention provides hard carbon materials comprising sp.sup.2 bonded graphite-like layers bonded together by sp.sup.3 three-dimensional diamond-like frameworks, wherein the whole carbon structure is stabilized with at least two alloying elements: the first alloying element selected from the group consisting of O, H, N, and a combination thereof; and the second alloying element selected from the group consisting of Si, B, Zr, Ti, V, Cr, Be, Hf, Al, Nb, Ta, Mo, W, Mn, Re, Fe, Co, Ni and a combination thereof. The graphite-like layers are mutually parallel with no azimuth order in-plane, and the diamond-like framework is fully amorphous. The ratio between graphite-like sp.sup.2 bonds and diamond-like sp.sup.3 bonds, and/or bonds between carbon and stabilizing elements may be gradually modulated forming a hierarchical structured material.
2. Description of the Prior Art
Structuring composite materials in micro, sub-micro, and nano scales constitutes one of the major areas of research in material engineering technology today. Such research combines different forms of carbon, including organic materials, nonorganic carbon-based materials, and diamond and/or diamond-like carbon to form composite materials exhibiting different physical properties.
Another area of research in the field of composite materials includes the hierarchical composites possessing a one-, two-, or three-dimensional artificially ordered structure. A traditional approach for hierarchical composite manufacturing is based on the combination of several known technologies to form composite components using the process of sintering to form artificial, bulk materials. However, approaches are limited by the structural resolution. At, or close to the structural resolution limits, the productivity of the composite declines, and the cost correspondingly grows. Consequently, many new technologies have recently emerged in an effort to create new and improved composite materials.
One such process which has been shown to be effective to the control nanoscale structure of the composite material is intercalation. This process comprises polymerization of the interlayer spaces of layered clay mineral, montmorillonite, followed by calcination of the folded silica sheets and organic cations, resulting in a highly ordered, mesoporous nanostructured material Fulushima, Yoshiaki, Toyota Central Res. & Development Lab Inc., Journal of Japan Society of Powder and Powder Metallurgy v. 41, No 10, 1984, p. 1189-1192, which disclosure is hereby incorporated by reference).
Intercalation, however, allows synthesis of specific structures only because this method is based on pre-manufactured crystalline materials which limits the design and manufacturing of artificial composite materials in both micro- and nano-scales. Because of this restriction, much effort recently has been employed toward the synthesis of amorphous-based composite materials by organic and/or nonorganic synthesis.
For example, polymer-derived micro-nano-structured Si.sub.3 N.sub.4 /SiC-composites were prepared by liquid-phase sintering or either amorphous, polymer derived Si-C-N powder or SiC coated Si.sub.3 N.sub.4 powder. However, following gas pressure sintering, the composites comprised nanosized SiC inclusions embedded in microcrystalline Si.sub.3 N.sub.4 grains (Greiner, Axel, Bill, Joachim, Riedel, Ralf, Max-Planck-Inst.; Proceeding of Materials Research Society, v 346, 1994, p. 611-616, Pittsburg, Pa., USA, which disclosure is hereby incorporated by reference).
U.S. Pat. No. 5,206,083 (1993) to Raj et al., hereby incorporated by reference, discloses diamond films deposited on a metal or ceramic composite comprising a matrix having dispersed therein finely divided diamond or diamond-like particles. These composites are useful in improving the erosion resistance of materials used for long wave infrared transmitting applications such as domes and infrared windows.
U.S. Pat. No. 4,948,388 (1990) to Ringwood, hereby incorporated by reference, discloses a diamond compact comprised of 60-95 volume percent of diamond crystals which have plastically deformed so that they form a rigid framework structure. The contacts between the diamond crystals occur over surfaces arising from plastic deformation of the diamond crystals during formation of the compact under pressure and temperature conditions within the graphite stability field. The diamond framework structure is bonded together by interstitial refractory carbide phases or metallic phases comprised of metal not forming carbides in the presence of carbon. The compact comprises less than about 2 percent volume of graphite and a compressive strength greater than 10 kbars.
U.S. Pat. No. 5,198,285 (1993) to Arai et al., hereby incorporated by reference, discloses a thin film of amorphous carbon-hydrogen-silicon comprising carbon and hydrogen as major components. The remaining composition comprises a silicon based material containing diamond-like carbon. The content of hydrogen is from about 30 to 50 atomic % weight. The content of carbon is about 70 atomic % weight or greater with respect to the total composition, except hydrogen and iron based metallic material. The film of amorphous carbon-hydrogen-silicon is very hard and has a small coefficient of friction.
U.S. Pat. No. 5,183,602 (1993) Raj et al., hereby incorporated by reference, discloses an improved carbon-metal composite comprising a carbon matrix and metal fibers distributed in the carbon matrix. The surfaces of at least a portion of the fibers are coated or alloyed with another material which has a tendency to form carbides which is equal or lower than that of metal constituting the metal fibers. The metal fibers are distributed in the carbon matrix in such a manner that their content varies along the thickness of composite, thereby imparting to the composite improved properties with respect to at least one of the following properties: mechanical strength, impact resistance, wear resistance, and electrical conductivity of a dispersion of small particles of diamonds in a matrix having infrared transmission properties and refractive index substantially similar to that of diamonds. The composites exhibit mechanical toughness and durability 2-4 times that of the similarly treated matrix alone without adverse effect on optical properties.
U.S. Pat. Nos. 5,352,493 (1994) to Dorfman et al., and 5,466,431 (1995) to Dorfman et al., which disclosures are hereby incorporated by reference, disclose a class of diamond-like materials formed from interpenetrating networks of carbon and alloying elements, as well as methods of fabricating such nanocomposite films. The films possess a unique combination of chemical and mechanical resistance, temperature stability, and wide range of electronic properties including low-temperature superconductivity. They may be used as protective coatings, electronic material, sensors, biocompatible materials. The method of these materials fabricating is based on co-deposition of the clusterless beams, wherein at least 50% of carbon particles comprise an energy above 100 eV, and the temperature of the substrate during the growth is less than about 500.degree. C. Common range of the carbon particles energy is 0.3 to 5 keV, and usually is about 1 to 1.5 keV, and the substrate temperature during the growth is less than about 200.degree. C. However, the growth rate is very limited, usually is in the range of 0.3 to 3.0 mm/h. Further, the material can be produced as a film, but its manufacturing requires a high-voltage power supply. Also, the hardness of these composite films is limited with about 20-22 GPa maximum, and usually does not exceeds about 12-15 Gpa.
Although this material is very stable against graphitization, during growth its structure is very sensitive to the particles energy and substrate temperature due to the possible graphite-like carbon forming. While Graphite is a layered substance whose structure and properties can be altered in a wide range, graphite is very fragile upon the application of mechanical stress, which is inherent to the week van der Vaals interaction between layers (Yudasaka et al., Yoshimura p-Electron Project, Japan; Appl. Phys. Lett. 64(7), 1994, which disclosure is hereby incorporated by reference). It has been recently demonstrated that interface between amorphous carbon and graphite usually creates unbonded radicals which weaken the structural rigidity of the materials, thereby providing a fracture path under stress (Yoon et al., Cambridge, Mass.; Interface Science, v. 3, 1995, p. 85-100, which disclosure is hereby incorporated by reference).
The present invention provides novel hard carbon materials which are believed to overcome the problems associated with the above described processes. The materials of the present invention comprise both, graphite-like and diamond-like carbon in a hierarchical structure, wherein the graphite-like layers are bonded together by the diamond-like framework such that the whole carbon structure is stabilized with at least two alloying elements. The materials of the present invention can be produced as coatings, as well as, bulk solid matter in a wide substrate temperature range using low voltage equipment. The growth rate of the materials of the invention can exceed 20 .mu.m/h, and hardness is usually in the range of about 20 to 35 GPa, but can exceed 50 Gpa. Elastic modules is usually in the range of about 150 to 250 Gpa, but can exceed 500 GPa.